1. Field of the Invention
The present invention relates to magnetic recording/reproducing apparatus used in cameras, which are adapted to record magnetic information on films, and reproduce magnetic information recorded on films. Magnetic information means information to be recorded magnetically or information which has been magnetically recorded.
2. Description of Related Art
Magnetic recording/reproducing apparatus of cameras are known which record magnetic information on films, and reproduce or read out magnetic information recorded on the films.
FIG. 18 shows the construction of a magnetic head used in a known example of magnetic recording/reproducing apparatus of a camera. In the known magnetic head, a recording coil 31 and a reproducing coil 32 are wound on a common core 33, and the coil 31 is exclusively used for magnetic recording while the coil 32 is exclusively used for magnetic reproduction. FIG. 18 also shows a bobbin 34, head cover 35, and a film 36.
FIG. 19A-FIG. 19C show various waveforms of current flowing through a coil containing 300 turns or loops during magnetic recording. More specifically, FIG. 19A shows a current waveform in the case where the film is transported or moved at a speed of 50 mm/sec., and FIG. 19B shows a current waveform in the case where the film is transported at a speed of 100 mm/sec. FIG. 19C shows an ideal current waveform.
The ideal waveform of the current flowing through the coil during magnetic recording has steep rises and falls as shown in FIG. 19C, but in practice the current rises and falls with a delay due to the inductance of the coil in actual. The inductance of the coil is proportional to the number of turns of the coil. Namely, the inductance is reduced with a decrease in the number of turns, and the recording current rises and falls more steeply or sharply as the number of turns of the coil is reduced.
Although rising and falling characteristics of the recording current do not change where the film transport speed at which the film is moved relative to the magnetic head is changed, rising and falling of the recording current, when observed on the basis of the film transport amount (or distance by which the film is moved), are delayed as the film transport speed is increased, as shown in FIG. 9B. As a result, the rising and falling of the recording current may not follow the film transport speed properly, and magnetic recording may not be normally performed.
In the meantime, a given magnetomotive force [AT] (ampere-turn) is needed for magnetically recording information on a magnetic recording medium of a film. If the number of turns of the recording coil is reduced so as to produce steep rises and falls of the recording current, the recording current must be increased so as to maintain the given magnetomotive force, which results in increased current capacity of a recording circuit, and increased power consumption.
Accordingly, the number of turns of the recording coil needs to be determined in view of all aspects of the film transport speed, current capacity of the recording circuit, power consumption, and the like.
FIGS. 20A and 20B show waveforms of current that flows through a coil during magnetic reproduction, wherein FIG. 20A shows a waveform of current that flows through a coil containing 1000 turns, and FIG. 20B shows a waveform of current that flows through a coil containing 100 turns.
Since the magnetic recording medium of the film has a very small intensity of magnetization, the S/N ratio is increased with an increase in the number of turns of the coil. When 1000-turn coil is used, for example, signal components and noise components can be clearly distinguished from each other even if noises are superposed on reproduced signals, as shown in FIG. 20A. When 100-turn coil is used, on the other hand, reproduced signals are obscured by noises, thus making it difficult to separate signal components from noise components.
As described above, the coil used for magnetic recording is desired to have a relatively small number of turns, so that the waveform of recording current, when plotted against the film transport amount or distance, shows steep rises and falls even at a high film transport speed, assuring increased reliability in magnetic recording operations. On the other hand, the coil used for magnetic reproduction is desired to have a relatively large number of turns, so that the S/N ratio is increased, assuring increased reliability in magnetic reproducing operations.
In the known magnetic head, therefore, the recording coil 31 containing a relatively small number of turns and the reproducing coil 32 containing a relatively large number of turns are wound on the common core 33, as shown in FIG. 18, such that the coal 31 is exclusively used for recording, and the coil 32 is exclusively used for reproduction.
In the known magnetic recording/reproducing apparatus of the camera, however, the recording coil and reproducing coil are separately provided as illustrated above, and therefore the size of the magnetic head is undesirably increased.